The present invention relates to a crane, in particular a bridge crane or gantry crane, which includes at least one crane girder that extends horizontally and is designed as a truss with a plurality of braces, on which girder a crane trolley with a lifting gear is movable.
German patent specification DE 260030 discloses a so-called double-girder gantry crane comprising two horizontal crane girders and two vertical support girders that form a gantry frame of the gantry crane. The crane girders extend in parallel and at a spaced interval with respect to one another. Arranged at lower ends of the support girders is in each case a travelling mechanism, by means of which the gantry crane is movable in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. A crane trolley having a cable winch is movable on and along the crane girders. In accordance with the design as a double-girder crane, a load picking-up means of the cable winch arranged on the crane trolley is lowered or raised between the two crane girders. The crane girders are designed as trusses and each comprise an upper boom and a lower boom that are each oriented horizontally and in parallel with one another. The upper and lower booms of the two crane girders are connected to one another by means of vertically extending, bar-shaped posts and diagonally extending, bar-shaped posts. At their ends, the two crane girders are connected to one another by means of crossbars and braces to form a frame. Bar-shaped posts and braces are provided along the longitudinal direction of the crane girders between the upper boom and the lower boom in the manner of a truss, which posts and braces each connect an upper boom to the lower boom arranged vertically therebelow.
German utility model document DE 1 971 794 U describes a double-girder bridge crane, whose two horizontal crane girders are connected to one another by means of head girders arranged at respective ends thereof and are movable together in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. Both crane girders are similarly designed as trusses and each comprise plate-shaped upper booms, bar-shaped lower booms and bar-shaped posts.
Patent specification DE 31 09 834 C2 relates to a tower crane having a mast and a crane jib that are designed as truss constructions. The cuboidal mast comprises four L-shaped and vertically oriented support girders, of which in each case two adjacent support girders are connected to one another by means of triangular plates. In this case, the plates are fastened with their corner regions and/or one of their sides to the support girders. At least some of the sides of the plates are folded and form stiffening ribs.
Furthermore, German laid-open document DE 1 759 120 A already discloses a crane girder that in a typical manner comprises an upper boom and a lower boom that are stiffened in the manner of a truss and by means of panels and are connected to one another. The panels are in the shape of a symmetrical trapezium and consist of sheet panels having bent outer contour edges. Two openings are also provided in the panel to reduce weight.
A further German laid-open document DE 1 907 455 A discloses a truss, whose upper boom and lower boom are connected by means of braces, which are formed in one piece from a flat profile extending in zigzag fashion. The flat profile has an angular, wavelike or channel-shaped cross-section.
Furthermore, U.S. Pat. No. 4,621,475 B already discloses a truss, whose braces are also designed as flat profiles that are folded back on both sides outside the ends. The thus flat ends of the braces are welded to upper and lower booms of the truss and the flat profiles extend on the whole in a vertical plane and in parallel with the longitudinal extension of the truss.
Laid-open document US 2005/0055951 A1 also discloses a further truss, whose braces comprise between the upper boom and the lower boom a cross-section that changes starting from the ends of the braces to the centre thereof.
German patent specification DE 1 095 486 B discloses a crane girder that is designed as a truss and comprises T-profiles as braces.
Furthermore, Chinese utility model CN 201 932 820 U and Korean patent application KR 2011 0020286 A disclose crane girders designed as box girders.